In a shared network, such as an Ethernet, a designated router (DR) is elected by a protocol independent multicast (PIM) protocol. An interface considers itself to be a DR by default after start-up. And after the interface receives a Hello message, DR is reelected to select a new DR. A message indicating that a user of an Internet Group Management Protocol (IGMP) or Multicast Listener Discovery Protocol (MLD) joins or quits a group will be received by all devices in the network, and the DR is responsible for forwarding multicast traffic to users in the network.
When a PIM device is newly added to the network, it is possible to cause a change of the DR. Specifically, when the newly added PIM device is elected as the DR, the original DR will not forward traffic. However, since the new DR does not learn full IGMP or MLD user information, packet loss will be caused. When the newly added PIM device learns the IGMP or MLD user information first, and then other PIM neighbors are discovered, there will be double traffics. The existing art is intended to perceive the change of the DR as earlier as possible to learn the IGMP or MLD user information as soon as possible, therefore the problem described above cannot be solved fundamentally.